Thank you OpenEnergyMonitor: Octopus Daikin ASHP monitoring

Ok. That’s a pretty key bit of missing info from before. In which case they’ve done exactly as youv’e asked and should have noted somethng to the effect on the MCS documentation that customer required the system to be set to constant temperature and fixed flow and the installers to leave site which is legit under MCS. :slight_smile:

If the default air change rate (assumes that you live in a barn with the doors open) in the MCS calculations wasn’t changed then you’ll probably have far higher assumed ventilation losses than you actually have.

Decent installers know this but are also unavailable for the most part. (too busy)

Compressors have a limited moudlation range through which they operate efficiently and have a long and happy life. Once they hit minimum output they must cycle. This is not a disaster if the system volumes / cycle times are long enoough.

Gas boilers are exactly the same but nobody pays the slightest attention.

The capacity of all units drop as the temperature drops.

Some units artifically limit the peak output at modest temperatures to make it look like “they maintain their rated output” all the way down to low temperatures. (Samsung HT Mon, Panasonic T-CAP etc) That’s all software limitations on compressor frequency though.

Your MCS handover documentation will tell you what the rated design temperatuer is and what the output of the unit is at that design temperature. The Octopus proposla docs are pretty good in this regard.

BlockquoteOk. That’s a pretty key bit of missing info from before. In which case they’ve done exactly as youv’e asked and should have noted somethng to the effect on the MCS documentation that customer required the system to be set to constant temperature and fixed flow and the installers to leave site which is legit under MCS. :slight_smile:

Honestly I didn’t think it was something I needed to explain.

I have no critcism of Octopus or their installation.

I did not bring up MCS requirements and what may not have been complied with.

I only the answered the question of what I started with and I did say I wanted them to go so I could set it up the WD curve myself.

My heat loss calculation was just over 6kWh at 21c inside and -3c outside.

It is about what I worked out myself and it includes a conservatory that I don’t need to heat and can close off if I want.

I didn’t want and would not have chosen a 9kW heat pump but I had no option with Octopus.

A `decent’ local installer wanted to install a 14kW Daikin here and when pushed he said I might get away with an 11kW!

You seem to be implying that Octopus are not decent installers, in fact I get that message all through your replies.

I appreciate your help but using this as a way to criticise Octopus is a little unfair,

The `decent’ installers that I contacted couldn’t even be bothered to quote. One wouldn’t even come here unless I agreed up front that I had at least £25,000 to spend on a Stiebl Eltron installation, not what I would call decent.

My installation is of a good quality, I checked as I was here all of the time. It may need some setting up but that is all.

About running longer.

I don’t understand why my heat pump stops heating so early. I have a WD curve set up which seems fine and I have a Madoka thermostat limiting the maximum room temperature. The thermostat also calls for heat, so why does my heat pump stop heating before the room temperature is reached?

Sorry fo being an idiot, I look at the data, the flow and return are separated but the heating stops, it waits 20 to 30 minutes and then starts again, why doesn’t it just carry on heating as it is already at the right temperature. Surely that would be more efficient?

Is this how it is supposed to work?

So perhaps I am a bit confused about how my heat pump should operate.

This is what I thought would happen.

With a WD curve and no room thermostat influence I thought that the water would be heated to a temperature based on the outside temperature and then pumped around my radiators until the return temperature matched the flow. At that point no heat is being passed to the house. If it’s too hot or too cold in the house I adjust the offset from the WD curve until I am happy.

With a WD curve and a room thermostat I thought the heat pump would pump the water round as before but just turn off when the desired room temperature was reached.

I don’t understand why the heat pump stops heating even though the flow and return temperature are suitably different and the requested room temperature has not been reached.

Maybe it is because I am looking at the data from my OpenEnergyMonitor system and the heat pump is seeing something else?

With the Daikin the room thermostat gives me a schedule option so I can adjust the temperatures for different times of the day.

Without the room thermostat control no schedules are available and the room temperature stays the same all the time the heating is on, basically 24 hours a day, which I don’t want, we want it cooler at night and I have not found a way to do this automatically with the Daikin MMI controller.

Which bits have I got right, if any, and which bits have I got wrong?

Whilst I am happy with how the heat pump is able to heat the house and the performance of our house as a whole (we’re not using much electricity) I am disappointed in the performance of the Daikin heat pump. I expected better COP figures at the flow temperatures I am running. If this is the best it can do then that is OK but its not very impressive. I have tried different options and nothing makes any real difference. Maybe the heat pump is too big or maybe Daikin heat pumps are just poor performers in terms of efficiency compared to others.

I have to say, when I look at the other heat pumps data no Daikin is performing very well.

This is quite normal for a heat pump, particularly when weather is mild or heat pump is over sized. The flow temperature has reached the temperature determined by weather compensation, and will continue to rise if it cannot shed that heat into the house. So it turns off and waits for the radiators to cool down a bit before starting another “cycle”. Here’s a view of mine today:

You can encourage your system to run for longer by opening all TRVs, or increasing the flow temperature. If your house is warm enough, then the system is working just fine as it is.



For the avoidance of doubt that is exactly what I am implying.

You were fortunate that they turned up and installed a heat pump. Over the road some chump monkey of an Octopus “engineer” surveyed a property, didn’t understand that it was a one pipe system, and the (contracted out) installer who arrived had to abandon the job with a “FFS you had one job” type opinion of his client. In other cases they’ve surveyed, arrived, actually started the job, then abandoned it leaving others to finidh.

You’ve found that it wasn’t setup. That seems to have been your decision. You’re now suggesting that it’s oversized too. That is also not entirely unexpected.

Others are finding that the Octopus installs don’t win any awards for in use performance either. (reference the league table that open energy monitor provides)

If you’re prepared to start with the assumption that they’re not particularly good at what they do you can troubleshoot the system. If you assume that the sun shines out of their backside and they know what they’re doing…then you’re not going to question all the decisions that ought to be questioned and you will get nowhere. That’s why I’m suggesting that you start with the assumption that the installer was at best an enthusiastic newbie and work from there.

It is not unfair or unreasonable to start with that assumption. They may have joined the pipes and wires very neatly. This does not make a quality installation though. (joining pipes and wires is the easy part)

Let’s go back to the beginning.

  • The temperature of the water sets the heat output from the radiators
  • The weather compensation curve sets the temperature of the water for a givne outdoor temperature
  • The compressor will run until the water is at the temperature the controls demand

That’s it on a basic system.

Sometimes there will be an error (undershoot or overshoot on room temperature)

What you are calling a “thermostat” is NOT a thermostat but a device for setting “room influence” [on water temperature]

  • The load compensation takes the room temperature vs the setpoint (works out the error) then tweaks the desired water temperature up or down to suit (room influence)
  • The compressor runs to maintain that desired water temperature.

If your weather compensation curve is too low, or your load compensation influence is too low, then the target water temperature will be too low. There probably isn’t ANY load compensation if the controls are set for fan coils.

Are you still on speaking terms with Octopus after you told them to go away before they finshed their work? If so, and you trust them to do a good installation, then the best option might be to as them to come back and commission the heat pump for you. Else what does the manual say?

If it continues to put heat into the water, even after the water is at the right temperature, then the water will be too hot.

Sometimes the radiators are able to emit ALL the heat the units puts into the water and so it can run continuously. Typically, if you’re designing for 45C at design condition with type 22s, and your radiators are capable of dissipating the full output of the heat pump when they are at 45C, then they will still be able to dissipate the minimum output of the heat pump when they are at say 30C.

If you are designing for higher temperatures at deisgn condition, then when you dial down the water temperature in the radiaotrs they are not able to emit enough heat even with the heat pump running at minimium output.

Also if your heat pum pis larger than the radiator area than you have, then evern if you are designing for say 45C at design condition the radiaotrs cannot emit enough heat even with the heat pump running at minimium output.

Think of this two ways:

  1. Your target water temperature is too low for the radiators to put enough heat into the proeprty to acheieve your target set point. Work out how to use the weather and load compensation controls to make this happen.

  2. Your radiators can’t kick out enough heat to let the heat pump run continuously even at it’s lowest output. Either somebody (and yes, I’m looking at Octopus) has fudged up the system design with far too big a heat pump on far too small a set of radiators; or there is somethign else amiss such as horrible balancing (they haven’t configured the hating system to ensure that each radiator gets the flow it needs - towel rails and auto bypass valves are classics for shortcutting water around a system) or user error (turning off radiators or using TRVs to limit temperature in too many rooms etc.

Share the Octopus design (the MCS calculations) and we can comment on #2. Invite them back to finish the job is easiest for #1; else you’ll need to become skileld enough to install Daikin units yourself?

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Thanks Tim.

All my TRV’s are wide open.

I does seem to operate like yours and most others. I just thought it would be more efficient and I must be doing something wrong.

I think I have just messed around a bit too much this week.

It’s working well as a heating system, it’s warm enough in here, and the cost is good.

I’ll leave it alone for a while and see how it performs in lower temperatures.

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I didn’t ask them to go away, we just agreed that I would set the WD curve, that was it.

I have changed the emitter setting to radiators.

There’s nothing wrong with my radiators, they are all pretty new and adequately sized and also well balanced according to the heat loss survey. It was done by Octopus but I can’t see any problem with it.

The rooms are all equally warm with the TRV’s wide open.

The heat pump is working OK by the looks of it, even comparing to other makes, that is in terms of how it operates.

The thing that is causing me doubt is the efficiency and looking at the `league table’ it seems that Daikin heat pumps are less efficient than most of the others.

I understand that if the water continues to be heated it will get hotter.

The bit I don’t understand is why the heat pump doesn’t add just enough heat to maintain the flow temperature.

Why does it have to get hotter and hotter and then turn off, why not heat up to the requested flow temperature and then maintain it until either the return is too hot or my Madoka controller (of the room temperature) tells the heat pump the house is hot enough and stop heating?

My heat pump is working as well as any other Dakin Altherma 3 that I can view, my house is warm and it was warm the first day I used it when the temperature was 3c outside here. It works and the cost of operation is OK compared to gas.

I don’t need to but I just wanted to improve the efficiency so it was as good as I could get it.

This seems to be as good as it gets with this heat pump.

That has helped me a lot. thank you.

I have a fundamental misunderstanding of how a heat pump works in this respect, and probably also a gas or oil boiler.

Looking at my data it appears the heat pump can only continue to increase the flow temperature, it cannot maintain a flow temperature.

I really thought it would heat to the flow temperature requested by the WD curve and then maintain it until the desired room temperature has been achieved.

What it actually does is heats to the WD curve flow temperature, shut down, cools down, and then has another go (and so on) until the desired room temperature is achieved assuming the flow temperature and emitter design is enough to achieve that.

If I want to achieve the desired room temperature in one hit then I need to increase the flow temperature via the WD curve.

The heat pump tries to add just enough heat to maintain the flow temperature, but given the fact that the minimum it can output is already reached and the house needs are even less, there is no other option than just stop so that the water temp doesn’t go too high needlessly.

This is what it does, but as the return increases the flow will increase as well because the HP is already at minimum. You cannot have a constant flow with the return matching it, as this means less heat transfer from the compressor, which in turns means less efficiency(which as you are discovering, with Daikin, is already less that it should be).

Again, this is the case because it’s already at minimum, and load is less than that.

Here you can see some data, but not as much as you would like to. The way I see it from the data shared, Daikins don’t have the efficiency stated on their papers, even more if the installation lacks perfection.
A bench test between a daikin,mitsu,vaillant,(other) would be something worth to have on this site @glyn.hudson @TrystanLea

In your case Matt, is looks like the 9kW model picked by them is a unit that is sold as a 9,11,14,16 range, in other words you have a 16 which is tweaked to be a 9, thus the modulation minimum efficiency cannot compare with a unit that is max 8-9kW. Saying that is looks like it can modulate really low 3.5-4kW but the efficiency is crap regardless. If you actually needed only a 6kW(your calculation) but ended up having a 14-16kW capable unit, then something is not right. So let’s get over a winter and then you will see how it goes for you.
By having a 14-16 as a 9er, you can be sure that it will put out the rated 9kW at any temp.


Radiators are not “balanced” by a heat loss survey. That’s radiator sizing.

Radiator balancing is making sure that the right amount of water goes through each radiator. A radiator twice the size needs twice the water flowrate etc.

You cannot tell this by looking a them by eye. You can tell this by staring the system up from cold and looking at them with an infra red camera. (they should all “fill up” with warm water and the same rate)

Do you know how Octopus did the radiator balancing?

The issue with that is you are conflating the heat pump AND the properties / installers when looking at the league tables.

Is it the heat pump that’s materially worse; or is it the type of person/property that buys it; or is it the installer?

Daikin is a quality product that one would not expect to see at the bottom of a league table. The Madoka controls are decent too.

Good Energy tend to install cheaper products. (Midea) You can be polite and suggest that they are perfectly adequate. You wouldn’t suggest that they are amazing. Yet their fleet average is apparently sCOPs in the mid threes. (data yet to be published)

Look at Glyn’s Gen6 Samsung or some of those Grant (Chofu) units. Nothing exotic but executed well.

I would not give up hope that decent performance can be extracted from a Daikin system based on what you see from untouched installations by large contractors. :slight_smile:

You see, this is something that plays role in how we see the efficiency of two different HPs at different load conditions, your pump consumption is higher that what we can see from other brands, same for another Daikin 9kW that is shared.
If your heat pump puts out 4000Wh using 900Wh including the high power consuming water pump that is a COP of 4.44ish
But if you would be to compare with other systems that looks like the water pump consumes only tens of watts, thus lets assume we take out 100Wh, a 4000Wh heat output using 800Wh will give a COP of 5.
Equally the lower the output the more of a difference in COP those 100Wh will make vs the higher/max output.
This tells me why the Daikin is/looks to be less efficient in reality, without taking in the account that we don’t know if in their certification paperwork, this high consumption of the water pump is included in their COP calculation/certification equation.


A heat pump CAN run continuously and maintain a set flow temperature IF the radiators can put out at least as much heat as the heat pump generates at minimum output.

Here’s a load of rough workings:
Knoll Pipe Calcs.xlsx (2.1 MB)

On the “heat pump” worksheet you can see the min/max output at various supply/return temperatures for various outside tempreatures.

Point 1)

The datasheet excerpts aren’t in English becuase English installers are considered f**king muppets by the manufacturer so they dumb down the English manuals to avoid person-in-blue-van or -erson-in-purple-van or person-in-red-van having heart failure.

You do want to know what the min and max outputs are if you’re designing though!

It’s also notbale that peak COP is NOT at minimum or maximum output but somewhere in-between. (that’s why they startup and shutdown instead of turning down furhter - it’s more efficient)

Point 2)

The “7 kW” unit is good for a max of 9 kW at -2C and can turn down to 3.5 kW at +12C

On the “Emitters” worksheet you can see each radiator and what the power output is / flowrate needs to be at certain temperatures.

At 45/40 they kick out 9.6 kW

At 35/30 they kick out 4.5 kW

So the heat pump can happily tick away constantly from flow temperatures of 45C down to something below 35C.

You can also see - if the balancing is correct and all that water is equally in motion - that there is 103 litres of water to heat up and cool down. At the minimum heat pump output (say 3.5 kW) the time it takes for that water to go from say 25C (with the radiators putting out maybe 1.5 kW) up to 30C (with the radiators putting out 3.5 kW) will be plenty (2 kW kettle boiling 1 litre of water 100 times? You’ll be there a while) The cycles will be long


These heat pumps should have REALLY long cycle times IF all the water in the system is actually in equal effect.

Chances are it isn’t. Chances are that a significant proportion of the water is short-circuiting through some radiators. The house still gets warm but your effective volume in circulation is small and the heat pump cycles away even when it shouldn’t be.

There’s also the possibilty that the 9 kW heat pump isnt’ conencted to 9 kW worth of radiators, so it’s haveing to “turn down” even when it’s fully cold out and then quickly runs out of “turn down” capability at part load.

So back to the question: what is the output of the radiators that this 9 kW Daikin heat pump are conencted to? If it’s less 9 kW that will be contributing to startup and shutdown; or the unit generally running away from it’s best efficiency point.

I can’t upload the radiator schedule from home, I would need to be at work.

But the total radiator output is 8,883 kWh at a design temperature of 50c

I am beginning to understand, thank you.

I am an accountant, not a heating engineer so this is not really my thing and I am doing my best

So it’s clear, my radiators are big enough to cover my house heat loss with a 50c and an outside temperature of -2.3c

This is what it was designed at.

It is also clear that my radiators are not big enough to handle the full output of my heat pump.

And that will get worse as I lower the flow temperature.

Not big enough to run as low as I was trying to.

Really the heat pump is too big for this house. I could correct it by getting a smaller heat pump or moving radiators around and increasing the size of some.

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Well adding up numbers it’s actually a big part in designing a system that matches the:
Numbers of the house with the numbers of a heat pump ending with the numbers of the radiators. :grinning:

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Thanks Vinny.

It makes sense.

It’s a shame that Octopus was the only installer I managed to get to quote.

I would have gone with anybody that would have quoted me to install a 7kW Vaillant as that was what I wanted.

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This is good place to be starting from :slight_smile:

Keep monitoring your system over the winter, making tweaks here and there, and learn what works best. Check out some of the other threads around this forum for more tips and tricks…


So you have convinced me that Octopus don’t really know what they are doing.

It hasn’t taken long for me to see the problems.

But it is not the installers, they just fit what they are told to and mine has been fitted well.

The problem is in the design, and maybe the choice of equipment.

I am sure the Daikin heat pump is of good quality but a quick look at the data from other heat pumps and it’s probably not the one you would choose.

My heat loss survey was not great, I had to help the surveyor quite a lot, my heat loss calculation was ridiculously wrong at his first attempt.

I think the problems also stem from what seems to be a box ticking exercise to comply with MCS requirements. It is all that seems to matter. To back that up I have an auditor coming on Monday to check the `quality’ of the installation. He will be getting an even bigger piece of my mind than I was planning!

So it seems I have a too big version of the wrong heat pump coupled with radiators that are too small, particularly when it is cool but not cold and the heat load is low.

The slightly better news is that it will probably work better on the few sub zero days we get and should be able to cope with the rare days when it gets to -10c.

I have learnt a lot today.

Thanks everybody.


I am going to ask to clarify that slightly.

Is that at “DT50” ?

This is the nominal output with the radiator at 80Cflow60C return (average 70C) and the room at 20C (hence 50C delta from average radiator to room)

Or is that at a supply temperature of 50C (and return temperature of…45C?)

Or is that at an average radiator tempreature of 50C (so supply 55C/return 45C?)

It makes a difference. Let’s see what their schedule says.

You are 300% more qualified than many plumbers then! :slight_smile: (numerate, literate, and above all interested)

If they are rated for 8.8 kW at 50/54 or 55/45 then that’s plenty big enough to handle almost the full output of the heat pump when they’re fuly hot.

We can guess at the minimum output from your heat pump even if the OEM doens’t provide it. 800W electrical input COP4 (probably about right), would put the minimum around 3.2 kW. COP6 (optimistic) would but it at 4.8 kW.

From this, and a guess of the water volume in the system, you can estimate when it will begin cycling and what the cycle times ought to be. If they’re shorter then you have a balancing issue.

Depending on what the contract says you could potentially demonstrate that it is to big (metering) and ask Octopus to swap it out for a more appropriately sized unit.

Or you could likve with it and mitigate the worst effects of oversizing by having your space heating circuit as balanced and open zoned as you can so that it runs for a reasonable time and performance doesn’t take a hit because of the cycling.

If you go back in history old boilers were range rated by the installers. They would dial down the flame so that it matched the maximum output of the radiators. (i.e. min boiler output = max boiler output = max radiator output) It would only run continuously if it was maximum cold outside. The rest of the time it would cycle. The purpsoe of the “range rating” was to keep those cycles as long as possible. (it would still work if it were left fialled up to 11; but the cycles would be short and efficiency would suffer) There’s really nothing new in this world!


On the contrary.

They know exactly what they are doing.

They’re operating at a loss (over investing in making their own equipment; losing money on installs to buy market share; giving away electricity at below cost for a period) to buy market share; whacking them in as fast as they can; doing what they can to clog up the airwaves and hoover up as much grant money as they can so that others don’t etc.

In phase two they start doing even lower performing high temperature installations, to reduce the capital cost of whacking them in and avoid losing money on that, but compensating for this by giving you a chepaer electricity tariff (lossmaking) for a while.

In phase three they withdraw the cheaper electricity tariff altogether, link it to some unneccessary expense such as annual servicing and care package etc, or make it only available to the original buyer etc.

All the while whipping up the fanboys in the press and governemnt. See also: Tesla, free supercharging, etc. :slight_smile:

You liked the installers. Most trades are liable I think. They come. They win against pipes and wires. They’re happy at winning. They give off good vibes.

The first part that appears to be lacking here is engineering. The surveyor needs to have a clue about (a) buildings and (b) heating systems. You can’t use a “make some stupid shit up and call it an EPC” type surveyor. They actually need to be serious and you actually need to spend serious money on them.

I think in the Octopus world you can give your mother an app and she becomes an expert on buildings and heating systems.

Perhaps not. Perhaps they would have worked out the heat loss and designed a heating system that’s able to work with the heat pump if you had left them alone. Probably not. Sounds like it would have been even worse.

MCS is pretty irrelevant. It’s sole purpose is to make it difficult to install heat pumps (it’s illegal to install one unless you’re an MCS union member; without having to go through planning) and to ensure that nobody can access grant finance except MCS members (i.e. rule one make sure you exist)

It’s completely ineffective because MCS will do very little s if the contractor doesn’t follow the scheme rules, especially if they’re a nice big fat bill payer like Octopus. We can see this through the DESNZ trials that showed Ovo / EON / Warmworks royally fudging up heat pump installs, metering these such that tey had proof of how fualty the installs were, and no remedial actions being taken.

Karma at your install haveing been selected for assessment. Evidently they thought you were their number one fan and have put it forward as their entry for assessment.

Will you be as nice as Joanna Lumley? :smiley:

“I think we are all agreed that Octopus didn’t know how to finish the heat pump installation at the time it was fitted, and their fitters needed to go do another job, so Octopus instructed the fitters toa gree to leave it in default settings in contravention of para 4.4.10 and were to confirm this in writing in their submission to MCS, with the intentiont o return and complete the commissioning to Daikin’s satisfaction and balance all the radiators blah blah”

Yep - you’ll be toasty.

Pleasure to chat with somebody as curious as you are :slight_smile:

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It just says design flow temperature 50c, when I spoke to them that is 50c from the heat pump.

Knowing what I now know, I think I have it set up nearly OK. It’s heating for an hour at a time, sometimes nearly two hours but less when it’s warmer, sometimes only 30 minutes.

But I think it’s nearly there, I can just up the flow temperature a bit so I get to the requested room temperature in one go more often.

It’s definately not short cycling in terms of on for 5 minutes, off for 5 minutes and then on again etc etc.

What I can do is move three radiators from downstairs to the upstairs, replace them with bigger and then increase the one remaining bedroom and the downstairs cloakroom.

That will add a lot more capacity to enable the heat pump to run at lower flow temperatures without providing more heat than the radiators can emit.

I will be explaining to Octopus what they have done, I’m sure it’s a waste of time though!

I think there will be days when I will be grateful to have this heat pump. I think my best plan is to increase the radiator capacity next spring/summer, a job I can do myself.

I was hoping to see COP’s between 3.50 and 4.00 during the heating season and I am really not that far from it.

I’m at 3.32 today and I have been experimenting. I have always said that I would be happy with anything 3.00 or above so it’s certainly not a disaster.